Technical Field
The present invention relates to a coil printed circuit board, a power reception module, a battery unit and a power reception communication module.
Background Art
As techniques for supplying electric power by wireless communication, an electromagnetic induction-type wireless power supply system, a magnetic resonance-type wireless power supply system and a radio reception-type wireless power supply system are known. For example, in a field of battery devices for charging second batteries incorporated in mobile devices such as cellular telephones, the electromagnetic induction-type wireless power supply system and the magnetic resonance-type wireless power supply system, in particular, are often used. In the electromagnetic induction-type wireless power supply system and the magnetic resonance-type wireless power supply system, wireless power transmission and wireless power reception are performed between a power transmission coil and a power reception coil. In International Standard “Qi” for the wireless power supply system, the wireless power transmission and the wireless power reception are performed in a frequency band of about 100 kHz to 200 kHz by the electromagnetic induction type.
The above-mentioned power reception coil is incorporated in the mobile device while being close to the second battery, for example. There are secondary batteries that markedly easily deteriorate in an environment of a temperature exceeding an allowable value such as lithium-ion batteries. Therefore, in order to prevent deterioration of such a secondary battery, a power reception coil that does not generate heat to a temperature exceeding an allowable value even when used in the frequency band of about 100 kHz to 200 kHz is required.
The larger a resistance component of the power reception coil is, the higher an amount of heat generation of the power reception coil during the wireless power supply is. Further, the resistance component of the power reception coil increases due to the skin effect and the proximity effect as the frequency increases.
In an air-core coil described in Patent Document 1, a wiring trace is spirally formed on one surface of an electrically insulating film. In this manner, the coil in which the spiral wiring trace is formed on only one surface of the electrically insulating film is referred to as a single-layer coil. The single-layer coil causes the proximity effect to be inhibited. Therefore, when the single-layer coil is used as the power reception coil, an increase in amount of heat generation of the power reception coil can be inhibited regardless of the used frequency band.
Patent Document 1: JP 2002-325013 A
Patent Document 2: US Patent Application Publication No. 2008/0262611 A1
Non-Patent Document 1: Xuehong Yu, Florian Herrault, Chang-Hyeon Ji, Seong-Hyok Kim, Mark G. Allen Gianpaolo Lisi, Luu Nguyen, and David I. Anderson, “Watt-Level Wireless Power Transfer Based on Stacked Flex Circuit Technology” Proc. Of 2011 Electronic Components and Technology Conference, pp. 2185-2191
Technical Problem
It is necessary to design a maximum outer diameter of the power reception coil incorporated in the mobile device to be smaller than the size of the mobile device. Therefore, when the above-mentioned single-layer coil is used as the power reception coil, it is difficult to increase the width, the space and the number of turns of the wiring trace. On the one hand, in the wireless power supply system, it is required to increase an amount of power that can be supplied per unit time. Thus, a charging time period of the secondary battery incorporated in the mobile device can be shortened.
In order to increase the amount of power that can be supplied per unit time, it is considered that current capacity of the single-layer coil is increased by an increase in thickness of the wiring trace.
However, dimension accuracy of the wiring trace decreases as the thickness of the wiring trace increases. Further, a formation process of the wiring trace is complicated as the thickness of the wiring trace increases. Therefore, it is difficult to actually use the single-layer coil as the power reception coil.
In a two-layer metal structure described in Patent Document 2, two spirally formed wiring traces are connected in series to each other and arranged to overlap with each other. The two-layer metal structure causes the two wiring traces to be laminated. Therefore, the number of turns of the wiring trace formed in each layer can be ½ as compared to the above-mentioned single-layer coil having the same maximum outer diameter. Thus, the width and the space of the wiring trace can be increased. Therefore, it is not necessary to increase the thickness of the wiring trace.
However, in the two-layer metal structure, a resistance value of the wiring trace in each layer increases due to the proximity effect. Further, a combined resistance value of whole of the wiring traces in the two layers is equal to the sum of the resistance values of the wiring traces in the two layers. Therefore, the resistance component of the two-layer metal structure increases as the frequency increases due to the proximity effect.
In contrast, in a flexible circuit described in Non-Patent Document 1, spirally formed four wiring traces are connected in parallel to each other and arranged to overlap with one another. The combined resistance value of whole of the four wiring traces connected in parallel is equal to a reciprocal of the sum of respective reciprocals of the resistance values of the four wiring traces. Therefore, even when the resistance value of the wiring trace in each layer increases due to the proximity effect, the combined resistance value of whole of the four wiring traces does not markedly increase.
However, in the flexible circuit of Non-Patent Document 1, two terminals for supplying currents to the four wiring traces are provided inside and outside of the spirally formed wiring traces. Therefore, when the flexible circuit of Non-Patent Document 1 is attached to a mobile device, it is necessary to connect a jumper wire to an inner terminal of the wiring trace. A connection work of such a jumper wire is complicated and supplies restriction to an assembly process of the mobile device.